So I've got a huge issue. I had a factory shifter on my car and using a factory plate to mount it to the transmission. It may be the same plate that has been on the transmission forever.

I'm mounting a new Hurst shifter on the car (purchase a new linkage kit and a new shifter assembly) and I can't get the old plate off. I can't put enough force onto the bolt with a normal allen wrench.

I'm going to try 3/8" drive allen sockets, but if they don't budge it I'd like to stop short of stripping the heads.

Any advice on how to do this in car without removing the entire transmission?